This invention relates to vascular access systems implanted in individuals for the infusion of medication, and particularly to vascular access systems which can be cleared of obstructions in place and methods for clearing such systems.
In the treatment of many illnesses it is necessary to infuse medication directly into the bloodstream periodically. To avoid having to locate a blood vessel for injection by a needle each time, it is desirable to implant a catheter into the circulatory system through which the medication is infused. To avoid having a catheter extend through the skin, which presents a danger of infection as well as considerable inconvenience and discomfort, the catheter is terminated at a vascular access port implanted beneath the skin and having a self sealing membrane penetrable by a needle for injecting the medication. Often, the medication is toxic in concentrated amounts and, therefore, must be infused through a catheter into a large volume of blood. To accomplish this, the catheter is fed through a vessel to a chamber of the heart. This combination of components is typically referred to as a vascular access system.
A problem that arises with implanted vascular access systems is that, despite steps taken after they are used to keep them clear, the catheter often becomes clogged with coagulated blood or other material between usages and is difficult to clear for use again. When there is an obstruction in an implanted infusion port there are basically two known approaches for solving the problem. One is to inject a dissolving agent such as heparin to try to dissolve the obstruction. Often this does not work, so the second approach must be used, which is to remove and replace the system. However, replacing the access system is dangerous, not only because it is an invasive procedure, but because removal of the system usually causes debris on the catheter to break away and enter the blood stream, which presents a risk of blockage of blood circulation to parts of the body.
One device previously known for clearing salt blockages in a drainage catheter is disclosed in Rumberger et al. U.S. Pat. No. 5,030,213, issued Jul. 9, 1991. However, this device is only suitable for a catheter whose proximal end extends outside of the body so that a router wire can be inserted into the catheter and a pin vice can be attached to the end of the catheter for rotating the router wire. Such a pin vice and router wire cannot be used with an implanted vascular access system.
Hawkins, Jr. et al. U.S. Pat. No. 4,790,812, issued Dec. 13, 1988, and Stevens U.S. Pat. No. 4,854,325, issued Aug. 8, 1989, both disclose devices and methods for removing an obstruction in a blood vessel. In Hawkins, Jr. et al. a cable with a cutting tip on its end is housed within a catheter which is inserted into the blood vessel. The cutting tip is pushed out the end of the catheter and rotated by the cable to fragment an obstruction. In Stevens, a guide wire is housed within a catheter inserted in the blood vessel so that the tip of the wire extends slightly beyond the tip of the catheter. The guide wire is caused to reciprocate at high speed to ram the tip through an obstruction. However, both of these devices and methods also employ a catheter whose proximal end extends outside the body and which would not be suitable for an implanted vascular access system.
Accordingly, there is a need for a vascular access system and clearing method for periodic infusion of medication wherein communication of the system with the exterior of the body is minimized and the catheter portion of the system may be cleared without removal of the system from the patient.